In the manufacture of reinforced concrete pipes in a vertical position, two different concepts are used that are generally referred to as (1), wet cast, and (2), dry cast.
In the wet cast operation, high slump concrete is used and is poured into a liquid tight form. The concrete mix generally stays in the form for 24 hours, so the concrete can harden. Then the forms and pallets are removed. Production is limited to the number of (expensive) forms and pallets that are available. This concept is well suited to producing very large pipe.
In the dry cast operation, no slump concrete is used in the formation of the concrete pipe. The jacket and core and sometimes the top pallet are removed immediately after the pipe has been formed.
In placing no slump concrete into vertical forms, generally, three different methods are used to densify the mix sufficiently, so that the pipe will not collapse when the forms are removed.
In the first dry cast method, the mix is placed into the forms and packed or densified by tamping in a tamping machine.
In the second dry cast method, the mix is placed in the form and is packed by rollers in a packerhead machine.
In the third dry cast method, the mix is placed in the forms and vibrated, causing the mix to turn into a semifluid mix and to settle and densify. Reference is made to U.S. Pat. Nos. 3,584,356 and 3,696,182.
When the vibration ceases, the fluid mix reverts back to a firm, dense, and relatively stable mix, so that forms can be removed immediately, without causing the newly made pipe to collapse.
The present invention relates in part, to the third method. In using the third method, the pipe is formed in the machine, and then the jacket and core, that are a part of the machine, are stripped from the pipe, leaving the pipe in the machine supported only by its bottom pallet.
Customarily, two procedures of moving the pipe from the machine to the curing area are utilized.
In the first procedure, the newly made pipe on its bottom pallet (with or without a top pallet) is slowly and carefully raised off of the machine's saddle by a fork truck, which then has to reverse to back out of the machine, then stop to shift gears, then turn to proceed to the curing area, then lower the pipe with its pallet to the floor, then reverse to clear the pipe and pallet, then stop and turn and proceed to the casting machine for another pipe.
In the second procedure the newly made pipe is moved out of the machine by an off-bearing apparatus, which inserts its forks under the outside edges of the bottom pallet, then raises the pipe with its bottom pallet, off of the saddle. Then the forks, which are attached to an overhead carriage which rides on an overhead track (rails), move the pipe and bottom pallet out from under the machine and lowers and deposits the pipe and lower pallet onto a moving floor that generally runs at right angle to the machine.
This apparatus, when automated, eliminates the need of a fork truck and operator.
In either procedure, the forks raise the pallet, with the forks being positioned on the outer circumference of the pallet. The weight of larger pipe will cause the section in the middle of the pallet to sag, progressively more, as pallet size increases. This sagging causes cracks and the pulling of the concrete away from the reinforcing wires, sometimes causing pieces of the green pipe to fall off, or the pipe to collapse.
These two systems of removing the forms from the pipe in the machine and then removing the pipe from the machine on only its bottom pallet, are well suited to pipes from 12" to 36" in dia., due to the fact that in these smaller sizes, the bottom pallets are relatively rigid.
In pipe of larger sizes, i.e. 48" to 96" plus, the difficulty of safely removing these sizes of pipe from the machine, becomes progressively greater as sizes increase.
Because of this sagging problem with larger pipe, another procedure is widely used, in which the forms are filled with no slump concrete at a central filling station, and vibrated. Then a top pallet is manually placed on top of the mix to form a tongue (or groove).
The pipe in this form is then transported by overhead crane or fork-truck to the curing area. The forms are manually removed and the pipe left standing on its bottom pallet.
The top pallets weighing as much as 400 lbs. are removed from cured pipe in the curing area by hooks attached to an overhead crane or fork-truck, then moved to an area adjacent to the filling station, then lowered and cleaned, then after the form is filled, the top pallet is raised and placed on top of the mix to form the tongue, then tranported again to the curing area. All of this is accomplished in close proximity to 3 or 4 men, which creates a hazardous situation.
The forms which have been removed from the pipe are manually reassembled around another bottom pallet with its reinforcing cage and the empty form and top pallet transported back to the filling station, and the cycle repeated.
In this procedure, the green pipe has the protection of the outer jacket, which also grips the outer circumference of the bottom pallet, preventing any flexing, while being moved to the curing stage. The loss of pipe due to breaking apart is minimal.
On the other hand, these current procedures are complex, slow, costly, and hazardous in producing and handling pipe of a larger size.
It is, therefore, an object of the present invention to provide an improved means of handling large, newly-made pipe from the forming machine through curing without harm to the pipe.
A further object of this invention is to provide a method and apparatus which simplifies the handling and moving of concrete pipe, both green and cured, with top and bottom pallets.
Another object of the present invention is to provide a method and apparatus which will reduce the number of personnel required to handle the newly-made pipe from forming machine through curing to storage.
A still further object of the present invention is to provide a method and apparatus which will render less hazardous the handling of pipe, both green and cured on pallets.
Another object of the present invention is to provide a less costly method and apparatus for handling both green and cured pipe.
A still further object of the present invention is to provide an apparatus for safely handling the precision top pallets that are compatable with the bottom pallets in making precision gasket joints.
A further object of the present invention is to provide an apparatus which will safely remove the top pallet from a cured pipe, clean, oil and then place it on a cage that is sitting on a pallet car, ready to be moved to a pipe machine.
A still further object of the present invention is to provide an apparatus for clamping, lifting, removing and rotating the cured pipe from the loop system.
A further object of this invention is to provide a system for the removal of pallets from cured pipe for substantially immediate re-use, and stockpiling pipe that were previously manufactured during current manufacturing.
A still further object of the present invention is to provide a system whereby the pallet cars are automatically positioned in designated respective positions, during the manufacturing and handling cycle.